SAW devices find utility in a number of different applications including resonators, filters and oscillators. Some advantages of SAW devices include small size, high device uniformity, temperature stability, and flexibility of device function. When using SAW devices in, for example, high frequency oscillator circuits, stable frequency characteristics are required. Therefore, the SAW oscillator must be protected from environmental contamination which can produce changes in the acoustic wave propagation velocity. Any change in velocity results in a change in the SAW delay time (the real time delay provided by the SAW) which in causes frequency shifting of the SAW oscillator. To prevent this outside contamination, vacuum encapsulation of the device is required.
Vacuum encapsulation of a SAW device involves packaging the device with a cover in a vacuum. Although vacuum encapsulation has solved the problem of contamination, problems associated with SAW packages can arise from temperature induced stresses caused from the difference in thermal characteristics of the device substrate and the package cover. As a result, the wave propagation velocity and the SAW time constant become distorted. Furthermore, where there have been matching thermal characteristics between the cover and the substrate as in "A Miniature Hybrid Circuit SAW Oscillator Using An All Quartz Packaged Resonator", by Montress et al., (1985 IEEE Ultrasonic Symposium Proceedings), and U.S. Pat. No. 4,213,104 to Cullen, high package cost has been a problem.